package cuppics;

import java.util.Arrays;

import org.junit.Test;

public class Prj25 {

	/**
	 * The Fibonacci sequence is defined by the recurrence relation:
	 * 
	 * Fn = Fn−1 + Fn−2, where F1 = 1 and F2 = 1. Hence the first 12 terms will
	 * be:
	 * 
	 * F1 = 1 F2 = 1 F3 = 2 F4 = 3 F5 = 5 F6 = 8 F7 = 13 F8 = 21 F9 = 34 F10 =
	 * 55 F11 = 89 F12 = 144 The 12th term, F12, is the first term to contain
	 * three digits.
	 * 
	 * What is the index of the first term in the Fibonacci sequence to contain
	 * 1000 digits?
	 */
	@Test
	public void test() {
		System.out.println(Calculator.calculate(1000));
	}

	public static class Calculator {

		public static int calculate(int bitsLimit) {

			int a[] = new int[bitsLimit];
			int b[] = new int[bitsLimit];

			a[a.length - 1] = 1;
			b[b.length - 1] = 1;

			int start = 3;

			while (true) {

				int[] c = sumArr(a, b);
				if (c[0] > 0) {
					break;
				}
				a = copyArrs(b);
				b = copyArrs(c);
				start++;

			}

			return start;

		}

		private static int[] copyArrs(int[] b) {
			return Arrays.copyOf(b, b.length);
		}

		private static int[] sumArr(int[] a, int[] b) {
			int[] ret = copyArrs(b);
			for (int i = 0; i < a.length; i++) {
				ret[i] += a[i];
			}

			for (int i = b.length - 1; i > 0; i--) {
				ret[i - 1] += (ret[i] / 10);
				ret[i] = ret[i] % 10;
			}
			return ret;
		}
	}
}
